Just something I noticed the day before fridays large sell-off.  About mid day thrusday we had been trending up all day, then a quick spike down came in with  the largest volume of the day before the market continued it’s rally higher took give the look of a very bullish day at the close. On friday as soon as that same area was re-tested the surge in selling came again. Black box selling?? who knows. Below you can see a 2 day 5 min chart of the S&P mini futures.